1. Field of the Invention
The invention relates to a jet pump with improved start-up properties. The jet pump can be used for the continuous supply of liquid fuel from remote containers or tanks to devices making use of the fuel. The invention further relates to the use of the jet pump in fuel delivery systems of internal combustion motor vehicles, especially in those systems which are equipped with a so-called saddle fuel tank.
2. Related Technology
Nowadays, saddle fuel tanks are widely used by the motor vehicle industry because of their greater fuel storing capacity compared to that of standard fuel tanks. Saddle fuel tanks are most frequently used with four wheel driven (4WD) and rear wheel driven vehicles and have two compartments connected by a channel located within the tank just above the saddle portion thereof. As a consequence of the two compartments, a special fuel delivery system should be installed in this type of fuel tanks to transfer the fuel from one of the compartments (“passive side”) to the other (“active side”) and then to the engine. To achieve this, in most cases in-tank fuel supply units are provided within the tank.
U.S. Pat. No. 6,619,272 describes an in-tank fuel supply unit to be mounted in the passive side of the fuel tank. The supply unit has a fuel pump in the fluid communication with a jet pump and pumps fuel from the passive side of the tank to the active side thereof when a second pump located in the active side is operating. Nevertheless, the jet pump can operate only if the fuel level is high enough to flood at least partially the mixing chamber of the jet pump. The jet pump cannot prime its mixing chamber by its driving flow, because all the flow collected in the mixing chamber is returned into the fuel tank when the fuel level is too low. Therefore, the operation of the jet pump is not independent of the fuel level; a well-defined minimal fuel level is required for the jet pump to start its operation. A further disadvantage of this solution dearly is the use of two fuel pumps, one in the active side and one in the passive side that makes the fuel delivery system more complicated and more expensive to manufacture. Furthermore, the use of two fuel pumps also raises the risk of a malfunction in the system.
In view of the background art, there is a need for such fuel delivery systems which are simple in construction, i.e. they contain active components only within the active side of the tank, reliable and cheap to manufacture. Furthermore, there is also a need for an improved jet pump that can be used in this type of the fuel delivery systems and enables reliable passage of fuel from the passive side of the saddle fuel tank, even if the fuel level within the tank is extremely low. In other words, there is a need for a jet pump being capable of operating independently of the fuel level within the saddle fuel tank.
The present invention achieves these objectives by providing a jet pump having a first inlet duct, a second inlet duct and an outlet duct having an outlet end, wherein said ducts are in fluid communication with each other at a central volume portion. The jet pump also comprises a sleeve formed with a closed end at the bottom and partially enclosing said outlet duct. The sleeve has a lateral opening therein at a predetermined height above the outlet end of the outlet duct. Furthermore, a continuous flowpath with different flow directions is present within the sleeve along the inner and outer surfaces of the outlet duct towards the lateral opening.